SELECT 
  * 
FROM 
  cscart_abt__ut2_less_settings 
WHERE 
  style = 'unitheme_new.less'

Query time 0.00018

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.35"
    },
    "table": {
      "table_name": "cscart_abt__ut2_less_settings",
      "access_type": "ALL",
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "0.25",
        "eval_cost": "0.10",
        "prefix_cost": "0.35",
        "data_read_per_join": "920"
      },
      "used_columns": [
        "section",
        "name",
        "value",
        "style"
      ],
      "attached_condition": "(`s2cart`.`cscart_abt__ut2_less_settings`.`style` = 'unitheme_new.less')"
    }
  }
}